Differentiation of the “Intermediate” Coli-Like Bacteria

Abstract

The "Intermediate" group constitutes a distinct section of the coli-form bacteria and may be differentiated from both Escherichia and Aerobacter. The "Intermediate" section differs from true Escherichia in that the former utilizes the citrate radical as a sole source of C in an otherwise inorganic medium; produces H2S in proteose peptone, ferric citrate agar; decomposes cellobiose; uses urea as a sole source of N but does not use uracil; does not grow well at 45-46[degree] C; and is not resistant to H3BO3. The "Intermediate" section may be differentiated from true Aero bacter in that the former does not produce acetylmethyl-carbinol from glucose; is methyl-red positive; generally produces H2S in proteose peptone, ferric citrate agar; does not utilize uric acid, uracil, yeast nucleic acid, allantoin or hydantoin as sole sources of N but does use urea; and does not decompose Na malonate. The "Intermediate" bacteria are most closely related to the organisms of the genus Escherichia from the standpoint of the physiol. similarity in the metabolism of glucose. For this reason the cultures studied were allocated to the genus Escherichia, stressing, however, that until the question of natural habitat of the "Intermediate" section has been more conclusively proved it is desirable to segregate such cultures from true E. coli which is conceded to predominate in the feces of vertebrates. On the basis of statistical correlation, 2 spp. of "Intermediate" coli-like bacteria were recognized. The predominant species, E. freundii, was represented by 196 cultures. The remaining 27 cultures were described as E. intermedium (Werkman and Gillen) nov. comb. A new description of E. intermedium is also given.